1. Field of the Invention
The present invention relates to an automatic focusing device for focusing an objective lens to an object by moving an optical system of the lens by a driving device in response to means for detecting the focusing state of the object, and more particularly to an automatic focusing device so constructed as to allow focusing to an object located within an arbitrarily selected distance range.
2. Description of the Prior Art
For the purpose of accelerating the focusing operation of an automatic focusing device particularly for a photographic camera, it is conceivable to divide the entire photographing distance range into a certain number of ranges, namely to divide the entire movable stroke of a photographing lens corresponding to said entire photographing distance range into a certain number of sections and to drive the photographing lens for focusing onto to an object in a selected distance range, thereby preventing unnecessary drive of the photographing lens which might be caused by a sudden entry of a different object into a distance-measuring area in the object field or by displacement of the distance-measuring area resulting from camera shake, or enabling focusing to a particular object among plural ones positioned at different distances along the photographing optical axis.
However, a structure involving simple division of the entire distance range into several ranges for example a far-distance range, a medium-distance range and a near-distance range, wherein a distance range containing a desired object is selected from thus divided ranges and the lens is moved only within the selected distance range is inconvenient in that such structure becomes unable to effect focusing particularly in case the object is positioned in the neighborhood of the boundary of two divided distance ranges and moves over the two ranges.